The Astrophysical Journal Supplement Series, 164:52–80, 2006 May # 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.
MULTIWAVELENGTH STAR FORMATION INDICATORS: OBSERVATIONS1,2 H. R. Schmitt,3,4,5,6 D. Calzetti,7 L. Armus,8 M. Giavalisco,7 T. M. Heckman,7,9 R. C. Kennicutt, Jr.,10,11 C. Leitherer,7 and G. R. Meurer9 Received 2005 May 31; accepted 2005 November 13
ABSTRACT We present a compilation of multiwavelength data on different star formation indicators for a sample of nearby star forming galaxies. Here we discuss the observations, reductions and measurements of ultraviolet images obtained with STIS on board the Hubble Space Telescope (HST ), ground-based H , and VLA 8.46 GHz radio images. These observations are complemented with infrared fluxes, as well as large-aperture optical, radio, and ultraviolet data from the literature. This database will be used in a forthcoming paper to compare star formation rates at different wave bands. We also present spectral energy distributions (SEDs) for those galaxies with at least one far-infrared mea- surements from ISO, longward of 100 m. These SEDs are divided in two groups, those that are dominated by the far-infrared emission, and those for which the contribution from the far-infrared and optical emission is comparable. These SEDs are useful tools to study the properties of high-redshift galaxies. Subject headinggs: galaxies: evolution — galaxies: starburst — infrared: galaxies — radio continuum: galaxies — stars: formation — ultraviolet: galaxies
1. INTRODUCTION In recent years, all wavelength regions have been exploited to track down star formation at all redshifts and trace the star forma- The global star formation history of the universe is one of the crucial ingredients for understanding the evolution of galaxies tion history of the universe. At high redshift the Lyman-break gal- axies (Steidel et al. 1996, 1999) provide the bulk of the UV light as a whole, and for discriminating among different formation from star formation, while SCUBA has been used to detect the scenarios (Madau et al. 1998; Ortolani et al. 1995; Baugh et al. brightest FIR sources in the range 1 P z P 3 4(e.g.,Bargeretal. 1998). Star formation is traced by a number of observables, often 1999, 2000; Smail et al. 2000; Chapman et al. 2003). The Lyman- complementary to each other. The ultraviolet (UV) is where the breakgalaxiesare,byselection,activelystar-formingsystems, bulk of the energy from young, massive stars is emitted, but it resembling local starburst galaxies in many respects (Pettini et al. suffers from the effects of dust extinction. The nebular emission 1998; Meurer et al. 1997, 1999), and possibly covering a large line H is a tracer of ionizing photons, and thus of young, mas- range in metal and dust content (Pettini et al. 1999; Steidel et al. sive stars, but it is also affected by assumptions about the stellar 1999; Calzetti 1997). The SCUBA sources occupy the high end of initial mass function. The far-infrared (FIR) emission comes from the dust-processed stellar light and reliably tracks star formation in the FIR luminosity function of galaxies (Blain et al. 1999), and are dust-rich objects. The relationship between the UV-selected and moderately to very dusty galaxies, but it is not a narrowband mea- FIR-selected luminous systems is not yet clear. Whether the two surement (like the UVor H ) and needs to be measured across the typesofgalaxiesrepresenttwodistinctpopulationsorthetwo entire infrared wavelength range. Finally, the nonthermal radio ends of the same population is still subject to debate (Adelberger emission is a tracer of the supernova activity in galaxies, but suf- & Steidel 2000). The answer to this question can drastically change fers from uncertain calibration. our understanding of the evolution, star formation history, and metal/dust enrichment of galaxies. 1 Based on observations made with the NASA/ESA Hubble Space Telescope, The difficulty in relating the two types of galaxies stems from which is operated by the Association of Universities for Research in Astronomy, the paucity of simultaneous UV, H , FIR(>100 m), and radio Inc., under NASA contract NAS5-26555. 2 data for both low- and high-z galaxies. While multiwavelength Based on observations obtained with the Apache Point Observatory 3.5 m observations of high-z galaxies are hampered at present by the telescope, which is owned and operated by the Astrophysical Research Consortium. 3 Remote Sensing Division, Code 7210, Naval Research Laboratory, 4555 sensitivity and positional accuracy limitations of current instru- Overlook Avenue, Washington, DC 20375; [email protected]. mentation, multiwavelength observations of local galaxies are 4 Interferometrics, Inc., 13454 Sunrise Valley Drive, Suite 240, Herndon, VA20171. possible and are key for producing the spectral energy distribu- 5 Visiting Astronomer, Cerro Tololo Inter-American Observatory, National tions (SEDs) that can be used as templates for higher redshift Optical Astronomy Observatories, which are operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. observations. To be representative, such SEDs should cover as 6 Visiting Astronomer Kitt Peak National Observatory, National Optical As- completely as possible the parameter range of properties (metal- tronomy Observatories, which are operated by AURA, Inc., under a cooperative licity, luminosity, etc.) of galaxies. agreement with the National Science Foundation. 7 This paper presents a large, homogeneous data set of multi- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD wavelength observations of 41 local (closer than 120 Mpc) star- 21218. 8 Spitzer Science Center, California Institute of Technology, Mail Stop 220-6, forming galaxies, spanning from the UV to the radio. The UV Pasadena, CA 91125. observations are from our own HST STIS imaging centered at 9 Department of Physics and Astronomy, The Johns Hopkins University, 1600 8. The optical (H ) and radio (6 cm and 21 cm) data are Baltimore, MD 21218. from ground-based programs complementary to the HST obser- 10 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721. vations. The FIR data are from archival Infrared Astronomical 11 Institute of Astronomy, University of Cambridge, Madingley Road, Satellite (IRAS) and Infrared Space Observatory (ISO) observa- Cambridge, CB3 0HA, UK. tions spanning the wavelength range 12–200 m. 52 MULTIWAVELENGTH STAR FORMATION INDICATORS 53
TABLE 1 Sample Characteristics
Velocity Distribution a ; b Name (J2000.0) (J2000.0) (km s 1) (Mpc) (arcmin) E(B V ) Morphology (1) (2) (3) (4) (5) (6) (7) (8)
ESO 350-38 ...... 0 36 52.5 33 33 19 6132 81.8 0.5 ; 0.3 0.01 Merger NGC 232...... 0 42 45.8 23 33 41 6682 89.1 1.0 ; 0.8 0.01 SB(r)a pec Mrk 555 ...... 0 46 05.6 01 43 25 4156 55.4 1.4 ; 1.2 0.02 SA(rs)b pec IC 1586 ...... 0 47 56.1 22 22 21 5963 79.5 0.3 ; 0.3 0.02 BCG NGC 337...... 0 59 50.3 07 34 44 1702 20.7 2.9 ; 1.8 0.08 SB(s)d IC 1623 ...... 1 07 47.2 17 30 25 6016 80.2 0.7 ; 0.4 0.01 Merger NGC 1155...... 2 58 13.0 10 21 04 4549 60.7 0.8 ; 0.7 0.04 Compact UGC 2982...... 4 12 22.6 05 32 51 5273 70.3 0.9 ; 0.4 0.14 Sm NGC 1569...... 4 30 49.3 64 50 54 40 1.6 3.6 ; 1.8 0.51 IBm NGC 1614...... 4 34 00.0 08 34 45 4681 62.4 1.3 ; 1.1 0.06 SB(s)c pec NGC 1667...... 4 48 37.1 06 19 13 4459 59.5 1.8 ; 1.4 0.06 SAB(r)c NGC 1672...... 4 45 42.1 59 14 57 1155 14.5 6.6 ; 5.5 0.00 SB(r)bc NGC 1741...... 5 01 37.9 04 15 35 3956 52.8 1.5 ; 1.0 0.06 Merger NGC 3079...... 10 01 57.8 55 40 49 1182 20.4 7.9 ; 1.4 0.00 SB(s)c NGC 3690...... 11 28 32.6 58 33 47 3121 41.6 3.0 ; 3.0 0.00 Merger NGC 4088...... 12 05 35.6 50 32 32 825 17.0 5.8 ; 2.2 0.00 SAB(rs)bc NGC 4100...... 12 06 08.7 49 34 56 1138 17.0 5.4 ; 1.8 0.01 (R’)SA(rs)bc NGC 4214...... 12 15 40.0 36 19 27 313 3.5 8.5 ; 6.6 0.00 IAB(s)m NGC 4861...... 12 59 00.3 34 50 48 880 17.8 4.0 ; 1.5 0.01 SB(s)m: NGC 5054...... 13 16 58.4 16 38 03 1630 27.3 5.1 ; 3.0 0.03 SA(s)bc NGC 5161...... 13 29 14.4 33 10 29 2247 33.5 5.6 ; 2.2 0.04 SA(s)c: NGC 5383...... 13 57 05.0 41 50 44 2333 37.8 3.2 ; 2.7 0.00 (R’)SB(rs)b:pec Mrk 799 ...... 14 00 45.8 59 19 44 3157 42.1 2.2 ; 1.1 0.00 SB(s)b NGC 5669...... 14 32 44.1 09 53 24 1387 24.9 4.0 ; 2.8 0.01 SAB(rs)cd NGC 5676...... 14 32 46.8 49 27 30 2237 34.5 4.0 ; 1.9 0.01 SA(rs)bc NGC 5713...... 14 40 11.3 00 17 26 1872 30.4 2.8 ; 2.5 0.03 SAB(rs)bc pec NGC 5860...... 15 06 33.4 42 38 29 5520 73.6 1.0 ; 1.0 0.01 Peculiar NGC 6090...... 16 11 40.8 52 27 27 8953 119.4 1.0 ; 1.0 0.00 Peculiar NGC 6217...... 16 32 39.3 78 11 53 1544 23.9 3.0 ; 2.5 0.04 (R)SB(rs)bc NGC 6643...... 18 19 46.0 74 34 09 1686 25.5 3.8 ; 1.9 0.06 SA(rs)c UGC 11284...... 18 33 35.5 59 53 20 8650 115.3 2.0 ; 2.0 0.05 Merger NGC 6753...... 19 11 23.4 57 02 56 3073 41.0 2.5 ; 2.1 0.06 (R’)SA(r)b Tol 1924 416...... 19 27 58.0 41 34 28 2863 38.2 0.8 ; 0.4 0.08 Peculiar NGC 6810...... 19 43 34.2 58 39 21 1888 25.3 3.2 ; 0.9 0.04 SA(s)ab:sp ESO 400-43 ...... 20 37 41.8 35 29 04 6032 80.4 0.5 ; 0.4 0.02 Compact NGC 7496...... 23 09 47.0 43 25 40 1623 20.1 3.3 ; 3.0 0.01 (R’)SB(rs)bc NGC 7552...... 23 16 11.0 42 34 59 1568 19.5 3.4 ; 2.7 0.01 (R’)SB(s)ab Mrk 323 ...... 23 20 22.7 27 18 56 4404 58.7 1.0 ; 0.7 0.05 SBc NGC 7673...... 23 27 41.3 23 35 23 3581 47.8 1.3 ; 1.2 0.04 (R’)SAc pec. NGC 7714...... 23 36 14.1 02 09 18 2925 39.0 1.9 ; 1.4 0.04 SB(s)b:pec Mrk 332 ...... 23 59 25.6 20 45 00 2568 34.2 1.4 ; 1.3 0.04 SBc
Notes.—Col. (1): Galaxy name. Cols. (2) and (3): Right ascension and declination, respectively, in J2000.0 coordinates. Col. (4): Radial velocities relative to 1 1 the Local Group. Col. (5): Distances obtained from Tully (1988) for the nearest galaxies, or calculated from the radial velocities assuming H0 ¼ 75 km s Mpc . Col. (6): Galaxies’ major and minor axis diameters (D 25). Col. (7): Galactic foreground reddening, obtained preferentially from Burstein & Heiles (1982), or from Schlegel et al. (1998) when the former was not available. Col. (8): Morphological types.
The data in this paper provide a uniform data set, in terms of icant variation between the final fluxes. The sample is composed type of data, reduction, and calibration strategies in each wave- of 41 galaxies, which were selected according to the following cri- length range, that will be used in an accompanying paper to reeval- teria: (1) IRAS 100 mfluxk1 Jy, to ensure detection with the ISO uate star formation rate indicators at the different wavelengths. long-wavelength camera; (2) recession velocity 9000 km s 1,to resolve spatial scales as small as 35 pc with STIS, which is the 2. SAMPLE scale of large OB associations or giant molecular clouds; (3) mean 0 The global list of galaxies in our sample is presented in Table 1, angular diameter D25 P 4 , to ensure that the sources were seen where we give their coordinates, radial velocities, distances, diam- as pointlike by the ISO long-wavelength camera; (4) L(H ) > eters, morphological types, and foreground Galactic reddening. 1039 ergs s 1 in the central 500 –1000,toselectactive,centrallystar- We gave preference to Galactic reddening values from Burstein & forming objects; (5) no, or at worst weak, nonthermal nuclear ac- Heiles (1982) instead of Schlegel et al. (1998), because for gal- tivity, as determined by the nuclear emission line properties of the axies with high foreground reddening, such as NGC 1569, the lat- galaxies (e.g., Ho et al. 1997). We retained only four of these ac- ter values result in too high a correction (i.e., an unphysically blue tive galaxies in our sample, those for which the nuclear spectrum spectrum). Nevertheless, this correction is usually very small, and (inner 200) shows emission-line ratios typical of active galactic the difference between the two values does not introduce a signif- nuclei (AGNs), while a more extended spectrum, encompassing a 54 SCHMITT ET AL. Vol. 164 region of 1000 or larger, has emission-line ratios typical of H ii re- tions of Mrk 555, which resulted in the drifting of the spacecraft. gions. Based on the comparison of the nuclear and integrated H This produced slightly elongated point sources, but did not affect or radio emission, we estimate that the AGN contributes to, at most, the integrated flux of this galaxy. 10% of the total luminosity in these galaxies. The reduction and calibration of the data followed standard Our sample specifically excluded ultraluminous infrared gal- procedures. The images of the galaxies in our snapshot project axies (ULIRGs), because data for a significant number of such were obtained in single exposures of 1320 s each. Only IC 1623 sources are available from the literature (Goldader et al. 2002), had its observations split into multiple exposures, which had to obtained in a instrumental configuration similar to ours. Our pro- be registered and combined. Background levels and standard ject aimed to cover the IR luminosity range of more normal gal- deviations ( ) were determined on emission-free regions of the axies, thus extending the low bound of this parameter by a factor images. The images were background-subtracted, clipped at the 103, in order to accommodate the fact that high-redshift galax- 3 level (pixels with flux lower than 3 were set to zero) and ies may not all be as IR-luminous as ULIRGs. Nevertheless, we flux calibrated using the information available in their headers. collected the data available on ULIRGs in the literature and will The UV fluxes of the galaxies, obtained by integrating the emis- take them into consideration in our analysis paper (Schmitt et al. sion in the final images, as well as the 3 detection limits, are 2006). given in Table 3. These values are not corrected for Galactic The final sample covers a wide range of intrinsic properties. extinction. The host galaxy morphologies vary from regular spiral galaxies to Throughout this paper we use the technique of measuring the interacting/merging systems. The bolometric luminosities, cal- fluxes of the images inside the 3 level, not by integrating every- culated based on the infrared luminosities and the correction fac- thing inside a given aperture. The reason for making a cut at the tor given by Calzetti et al. (2000), vary by a factor of almost 1000, 3 level is to avoid spurious background variations and flat- 8 with NGC 1569 having Lbol 7 ; 10 L , while IC 1623 has fielding errors. We test the effect of this technique on the fainter, 11 4:7 ; 10 L , close to the ULIRG limit. This sample also covers lower surface brightness sources by comparing measurements a large factor in star formation activity, from the poststarburst in of both H and UV done in this way with measurements done NGC 1569 up to the FIR-luminous starburst in IC 1623; as well as without clipping the images at the 3 level. We find that in most afactorof 10 in metallicity, from metal-poor galaxies such as cases the difference between the two techniques is negligible, Tol 1924 416, which has ½O/H ¼8:0, to metal-rich ones such while in the worst cases it can represent a 5% difference in the as NGC 7552, which has ½O/H ¼9:3 (Storchi-Bergmann et al. total H flux, well within our measurement uncertainties (see 1994). Although this sample covers a wide range of intrinsic prop- below). Another way to estimate that this approach will cause an erties, one should keep in mind that it was culled from the ISO insignificant error to the integrated fluxes is based on the fact that archive, so the galaxies may have been observed because of some the area covered by pixels between 3 and 6 is small, as can be characteristic of particular interest for the original observers. As a seen in the figures, suggesting that the area associated with the result, the final sample may not necessarily be representative of object and covered by pixels below 3 should also be small. typical galaxies. Combining this information with the fact that the 3 flux level Complete UV-H -radio coverage is achieved for 26 out of is very small compared to the regions where the bulk of the 41 galaxies, due to various limitations (e.g., snapshot nature of the emission originates, indicates that this approach will not change HST observations, weather, declination of the source). Complete the measured flux significantly. The errors involved in the UV flux coverage using our own data was obtained for 13 galaxies, with measurements are of the order of 5%. These errors are mostly due the other 13 using literature data to supplement our own data. For to the stability of STIS and the accuracy of the flux calibration. an additional 11 galaxies we have data for 2 of the 3 wavelengths We estimate that the contribution from Poisson noise to the error (UV,H ,orradio). budget is very small, accounting to less than 1% even in the case of the fainter galaxies observed (NGC 3079 and NGC 4088). For 3. OBSERVATIONS AND REDUCTIONS simplicity, we assume a uniform 5% flux error for all sources. In this section we present the details of our multi-wave-band 3.2. H Observations observations, reductions, and measurements. We also present The H images presented in this paper were obtained in four ultraviolet, optical, infrared, and radio data collected from the lit- observing runs on three different ground-based telescopes: the erature, which are complementary to our observations and will Apache Point Observatory (APO), Kitt Peak National Observa- be used in a forthcoming paper. Table 2 presents the details of the tory (KPNO), and the Cerro Tololo Inter-American Observatory different observations. (CTIO). We also use archival HST narrowband images of NGC 1569 and NGC 4214. These images were complemented with 3.1. Ultra iolet Obser ations v v large-aperture H fluxes from the literature, available for several Ultraviolet images were obtained for 22 of the galaxies in our galaxies that we could not observe. sample ( 50%), using STIS on board the HST. The observations The APO observations were done with the 3.5 m telescope on of 21 of the galaxies were done as part of the snapshot project the second half of the night of 2000 July 3/4. We used SPIcam, bin- 8721 (PI: D. Calzetti), using the FUV-MAMA detector and the ning 2 pixels in both direction, which gives a scale of 0B28 pixel 1 filter F25SRF2. We also obtained HST archival data for IC 1623, and a field of view of 4A8 ; 4A8(1024; 1024 pixels). Two filters which was observed with the same configuration by the project were used for these observations, one centered at 6450 8 with a 8201 (PI: G. R. Meurer). The names of the data sets in the HST bandwidth of 100 8, and one centered at 6590 8 with a bandwidth archive and exposure times of the images are given in Table 2. of 25 8. These filters were used for continuum and line obser- Our images have a pixel size of 0B025 and a field of view of vations, respectively. The continuum observations consisted of 2500 ; 2500 (1024 ; 1024 pixels). The filter used for these ob- two exposures of 300 s for NGC 6217 and two exposure of 90 s servations (F25SRF2) is centered at k1457 8, and has a band- for NGC 6643. The on-band exposure times are given in Table 2. width of 284 8, which is slightly contaminated by geocoronal We also observed spectrophotometric standard stars from Oke O i k1302 8. Guiding problems happened during the observa- (1990). No. 1, 2006 MULTIWAVELENGTH STAR FORMATION INDICATORS 55
TABLE 2 Observations
Ultraviolet H Radio
Exposure Exposure Exposure Name Data Set (s) Observatory (s) Filter Configuration (s) Proposal (1) (2) (3) (4) (5) (6) (7) (8) (9)
ESO 350-38 ...... CTIO 3600 6680/100 BnA 5840 AJ 176 ...... BnA 3750a AJ 176 NGC 232...... CTIO 3600 6680/100 CnB 1670 AS 713 Mrk 555 ...... O63X04WWQ 1320 WIYN-2 720 KP 1494 C 1700 AS 713 IC 1586 ...... C 1650 AS 713 NGC 337...... CTIO 3600 6600/75 C 1680 AS 713 IC 1623 ...... O5CU02010b 3051 ...... CnB 1680 AS 713 NGC 1155...... CnB 1690 AS 713 UGC 2982...... C 1650 AS 713 NGC 1569...... O63X09HYQ 1320 HSTc 1600 F656N B 3910 AA 116 NGC 1614...... C 1710 AS 713 ...... C 1020 AK 331 NGC 1667...... O63X36ITQ 1320 WIYN-2 720 KP 1494 C 1670 AS 713 NGC 1672...... O63X11R0Q 1320 ...... NGC 1741...... O63X38FIQ 1320 WIYN-2 480 KP 1494 C 990 AK 331 ...... B 1770a AM 290 NGC 3079...... O63X35ZXQ 1320 ...... CnB 3050 TT 1 NGC 3690...... C 3740 AS 568 NGC 4088...... O63X12FMQ 1320 WIYN-1 480 W015 C 5380 AL 383 NGC 4100...... C 1680 AS 713 NGC 4214...... O63X39ESQ 1320 HSTd 1600 F656N C 590 AS 713 NGC 4861...... O63X40H7Q 1320 ...... C 1670 AS 713 NGC 5054...... C 1700 AS 713 NGC 5161...... CTIO 3600 6600/75 C 1690 AS 713 NGC 5383...... O63X16UKQ 1320 ...... C 1710 AS 713 Mrk 799 ...... O63X17DRQ 1320 WIYN-1 720 W016 C 560 AS 713 NGC 5669...... O63X18AVQ 1320 ...... C 1700 AS 713 NGC 5676...... O63X19LSQ 1320 ...... C 1680 AS 713 NGC 5713...... O63X20FBQ 1320 ...... C 1690 AS 713 NGC 5860...... O63X21OUQ 1320 WIYN-1 720 KP 1495 C 1690 AS 713 NGC 6090...... WIYN-1 720 KP 1496 CnB 1650 AS 713 NGC 6217...... O63X23BUQ 1320 APO 1200 6590/25 CnB 1660 AS 713 NGC 6643...... O63X24IAQ 1320 APO 1200 6590/25 CnB 1680 AS 713 UGC 11284...... O63X25Y6Q 1320 ...... CnB 1680 AS 713 NGC 6753...... CTIO 4500 6600/75 ...... Tol 1924 416...... CTIO 3600 6600/75 CnB 1690 AS 713 NGC 6810...... CTIO 3600 6600/75 ...... ESO 400-43 ...... O63X29FKQ 1320 CTIO 3600 6680/100 CnB 570 AS 713 ...... BnA 3160a AJ 176 NGC 7496...... CTIO 3600 6600/75 CnB 1640 AS 713 NGC 7552...... CTIO 3600 6600/75 CnB 1650 AS 713 ...... A 1590e AS 721 Mrk 323 ...... O63X31GSQ 1320 WIYN-2 960 KP 1494 C 1680 AS 713 NGC 7673...... C 1670 AS 713 NGC 7714...... C 1680 AS 713 Mrk 332 ...... O63X34AHQ 1320 WIYN-2 720 W016 C 1670 AS 713
Notes.—Col. (1): Galaxy name. Cols. (2) and (3): Ultraviolet HST data set name and exposure time. Cols. (4)–(6): Observatory where the H images were obtained ( WIYN-1 and WIYN-2 correspond to the 2001 May and November observing runs), the exposure time of the images, and the name of the filter used for the line observations. Cols. (7)–(9): VLA configuration in which the galaxies were observed, exposure times, and the code of the proposal from which the data were obtained. a These observations were done at 4.89 GHz. b Ultraviolet observations of IC 1623 consist of three exposures (O5CU02010, O5CU02020, and O5CU02030) obtained as part of the HST project 8201 ( PI: G. R. Meurer). c Archival HST data from project 8133 (PI: P. L. Shopbell). d Archival HST data from project 6569 ( PI: J. W. MacKenty). e This observation was done at 1.49 GHz.
The CTIO observations were done with the 1.5 m telescopes H observations are given in Table 2. We also obtained broad on the nights of 2000 August 01/02–08/09. We used the focal R-band images for each of the galaxies, which were used to ratio f/13.5 and the detector Tek 2k No. 6, which gives a scale subtract the continuum contribution from the line images. These of 0B24 pixel 1 and a field of view of 8A2 ; 8A2 (2048 ; 2048 broadband images were usually split into three exposures of pixels). The filters and integration times used for the narrowband 500 s each. We observed spectrophotometric standard stars from 56 SCHMITT ET AL. Vol. 164
TABLE 3 Ultraviolet and H Fluxes
8 cor cor ii Name F(1457 ) 3 F(H )int F(H )int F(H )match F(H )match 3 [N ]/H Area Reference (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
ESO 350-38 ...... 33.26 3.33 27.11 2.71 ...... 7.1 0.17 1.5 1 NGC 232...... 4.08 0.41 2.08 0.21 ...... 4.7 0.72 9.2 2 Mrk 555 ...... 1.43 2.8 9.06 0.91 6.66 0.67 3.72 0.37 2.73 0.27 5.1 0.27 ... 3 IC 1586 ...... 2.29 0.22 2.29 0.22 ...... 0.21 143.1 4 NGC 337...... 32.09 3.21 24.32 2.43 ...... 12.0 0.24 16.0 5 IC 1623 ...... 6.58 1.6 ...... 0.30 5.2 6 NGC 1569...... 1.73 7.2 151.85 15.20 151.09 15.10 136.00 13.60 135.30 13.50 50.0 0.04 8.0 7 NGC 1614...... 10.69 1.07 10.69 1.07 ...... 0.44 143.1 4 NGC 1667...... 1.07 1.7 9.18 0.92 5.14 0.51 4.58 0.46 2.47 0.25 9.7 0.69 200.0 8 NGC 1672...... 3.89 2.5 17.70 1.77 17.70 1.77 17.70 1.77 17.70 1.77 ... 0.46 200.0 8 NGC 1741...... 3.95 3.7 12.17 1.22 10.73 1.07 10.20 1.02 9.00 0.90 8.0 0.10 ... 9 NGC 3079...... 0.46 19.3 ...... 1.59 8.0 7 NGC 3690...... 89.13 8.90 89.13 8.90 ...... 0.40 8.0 7, 10 NGC 4088...... 0.67 13.5 62.14 6.21 47.85 4.79 4.36 0.44 3.36 0.34 2.2 0.32 8.0 7 NGC 4214...... 18.36 5.7 83.16 8.32 81.66 8.17 76.80 7.68 75.02 7.50 4.0 0.07 8.0 7 NGC 4861...... 13.07 2.4 19.75 1.98 19.75 1.98 19.75 1.98 19.75 1.98 ... 0.09 143.1 4 NGC 5161...... 9.21 0.92 7.09 0.71 ...... 17.3 0.36 19.6 5 NGC 5383...... 1.08 1.6 43.70 3.60 43.70 3.60 24.20 0.90 24.20 0.90 ... 0.36 8.0 7, 11 Mrk 799 ...... 0.57 7.9 12.80 1.28 8.44 0.84 4.28 0.43 2.82 0.28 4.0 0.50 19.6 2 NGC 5669...... 1.09 13.4 ...... 0.28 8.0 7 NGC 5676...... 0.37 8.9 23.56 2.30 23.56 2.30 ...... 0.45 8.0 7, 12 NGC 5713...... 1.53 28.2 ...... 0.47 16.6 13 NGC 5860...... 1.01 26.9 3.02 0.30 1.83 0.18 3.02 0.30 1.83 0.18 2.1 0.49 143.1 4 NGC 6090...... 8.67 0.87 6.29 0.63 ...... 3.3 0.45 143.1 4 NGC 6217...... 1.86 3.0 20.45 2.05 18.47 1.85 7.99 0.80 7.21 0.72 2.5 0.64 143.1 4 NGC 6643...... 0.80 47.4 29.58 2.96 28.07 2.81 4.37 0.44 4.15 0.42 6.4 0.32 8.0 7 UGC 11284...... 1.07 44.3 ...... 0.38 7.2 2 NGC 6753...... 22.60 2.26 22.60 2.26 ...... Tol 1924 416...... 19.05 1.91 18.82 1.88 ...... 6.5 0.02 200.0 8 NGC 6810...... 18.36 1.84 11.86 1.19 ...... 5.9 0.53 8.0 5 ESO 400-43 ...... 3.57 43.0 14.25 1.43 13.35 1.34 14.10 1.41 13.21 1.30 11.2 0.05 ... 14 NGC 7496...... 33.00 3.30 20.72 2.07 ...... 17.5 0.48 200.0 8 NGC 7552...... 71.00 7.10 41.61 4.16 ...... 15.6 0.57 200.0 8 Mrk 323 ...... 0.79 34.3 2.88 0.29 2.88 0.29 2.13 0.21 2.13 0.21 6.6 ...... NGC 7673...... 6.08 0.60 6.08 0.60 ...... 0.23 143.1 4 NGC 7714...... 27.96 2.80 27.96 2.80 ...... 0.36 143.1 4 Mrk 332 ...... 1.37 5.2 13.58 1.36 7.33 0.73 9.22 0.92 4.98 0.50 4.4 0.64 8.0 7
Notes.—Col. (1): Galaxy name. Col. (2): Ultraviolet flux, in units of 10 14 ergs cm 2 s 1 8 1, not corrected for Galactic extinction; the accuracy of the fluxes is of the order of 5%. Col. (3): 3 detection limit of the UV images in units of 10 20 ergs cm 2 s 1 8 1 pixel 1.Col.(4):IntegratedH flux, not corrected for [N ii] k6548, 6584 8 contamination, in units of 10 13 ergs cm 2 s 1.Col.(5):IntegratedH flux, corrected for [N ii] contamination. Except for NGC 6217 and Mrk 323, galaxies with identical values in cols. (4) and (5) correspond to values obtained from the literature. Col. (6): H flux measured inside an aperture matching that of the UVimage, not corrected for [N ii] k6548, 6584 8 contamination, in units of 10 13 ergs cm 2 s 1. Note that the values for NGC 1672 and NGC 5383 were obtained from the literature and are not contaminated by [Nii]. Col. (7): Same as col. (6), but corrected for [N ii] contamination. Col. (8): 3 detection limit of the H images, in units of 10 18 ergs cm 2 s 1 pixel 1.Col.(9):[Nii]/H emission line ratio. Col. (10): Area of the slit used to observe the [N ii]/H ratio. For ESO 400-43, the observations were centered at the nucleus, but the observed area was not given in the paper. NGC 1741 was observed with a slit 1B5 wide, but the length of the extraction was not available. Mrk 555 was observed with a slit narrower than 800, but the size of the extraction was not available. Col. (11): References from which we obtained the emission line ratio [N ii]/H , and for those galaxies for which we did not obtain images, the H flux. References.—(1) Kewley et al. 2000; (2) Veilleux et al. 1995; (3) Terlevich et al. 1991; (4) McQuade et al. 1995; (5) Veron-Cetty & Veron 1986; (6) Corbett et al. 2003; (7) Ho et al. 1997; (8) Storchi-Bergmann et al. 1995; (9) Vacca & Conti 1992; (10) Armus et al. 1990; (11) Sheth et al. 2000; (12) Kennicutt & Kent 1983; (13)Kewleyetal. 2001; (14) Fairall 1988.
Stone & Baldwin (1983) and photometric standards from Landolt tinuum subtraction. The narrowband images were calibrated using (1992) for the calibration of the narrow- and broadband images, observations of spectrophotometric standards from Oke (1990), respectively. while the broadband ones were calibrated using standard stars The KPNO observations were done with the WIYN 3.5 m from Landolt (1992). telescope on two different runs, on the nights of 2001 May 16/17– The data reductions followed standard IRAF procedures, which 18/19, and 2001 November 05/06–06/07 (we refer to these runs started with the overscan and bias subtraction, and the division of as WIYN-1 and WIYN-2, respectively, in Table 2). We used the the images by normalized flat fields. The individual images of Mini-Mosaic, which gives a pixel scale of 0B14 pixel 1 and a field each galaxy were aligned, convolved to bring both the line and of view of 9A6 ; 9A6(4096; 4096 pixels). The filters and integra- continuum images to a similar PSF size, and combined to elimi- tion times used for the narrowband H observations are indicated nate cosmic rays. The background was determined from emission- in Table 2. As for the CTIO observations, we obtained two or three free regions around the galaxy, fitted with a polynomial function images of 120 s each in the R band, which were used for the con- to eliminate residual illumination gradients, and subtracted. The No. 1, 2006 MULTIWAVELENGTH STAR FORMATION INDICATORS 57 data were calibrated using the standard star observations, and observed [N ii]/H ratios, the redshifts of the galaxies, and on- the World Coordinate System, obtained from stars in the field of band filter transmission curves used to observe them. Note that the galaxy, was added to the image headers. Whenever needed, the these corrected values are likely to be a lower limit of the real flux, fluxes were also corrected for redshift effects, taking into account since the observed emission-line ratio may still be dominated by where the H line fell on the transmission curve of the filter. the brighter regions of emission. Since these regions are usually The continuum subtraction was done in two different ways. related to the nucleus, which has higher metallicity, they should For the APO observations, the continuum images were not con- also have higher [N ii]/H ratios. taminated by line emission. In this case, these images were scaled Finally, we estimate the errors in our flux measurements. to match the width of the line filter, and then subtracted. We con- A significant part of the error comes from the flux accuracy of firm, by checking stars around the galaxy, that this procedure did the calibration stars, which is of the order of 4%–5%. Other not over or undersubtract the continuum. For all the other observa- effects that can introduce errors of a few percent in the fluxes are tions, we used a similar technique for the continuum subtraction, residuals from the flat-field correction, variations of the sky but had to do it recursively. Since the R-band images, which were transparency overnight, uncertainties in the Galactic foreground used for the continuum, are contaminated by line emission (1.5% reddening correction, and residuals from the sky and continuum of the integrated flux on average), they have to be corrected for subtraction. Poisson noise can also introduce some uncertainties this contribution to their flux; otherwise, a simple subtraction of the in the flux measurements, but this source of error is much smaller scaled R-band image from the line image will underestimate the than 1% in our case. Taking all these sources of error into ac- total H flux. The recursive subtraction was done by first sub- count, we make the conservative assumption that the error in our tracting the scaled continuum image from the line image; then the flux measurements is of the order of 10%. resulting line image was scaled and subtracted from the contin- 3.3. Radio Obser ations uum image, to remove the emission line contribution to this im- v age, and the corrected continuum image was used to subtract the The 8.46 GHz (3.5 cm) radio observations of most of the gal- continuum emission from the original line image. This process was axies in the sample were done with the VLA in two different repeated a few times, until the H and continuum fluxes in regions runs, both part of the project AS 713. The first run was 7 hr long, affected by contamination changed by less than 0.5% between during the CnB configuration, on 2001 June 24. We observed consecutive iterations. This indicated that the process had con- galaxies with <